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Structure of Woody Plants (Vascular Cambium (Ray Initials (shorter than…
Structure of Woody Plants
Vascular Cambium
Initiation of the Vascular Cambium
Vascular cambium
meristem that produce secondary plant body
interfascicular cambium
connects to fascicular cambium
Fascicular cambium
bundle of cells
Fusiform Initials
long, tapered cells
Periclinal walls
fusiform initials undergo
longitudinal cell division
produces 2 elongate cells
Anticlinal walls
perpendicular to cambium's surface
Ray Initials
shorter than fusiiform
more or less cuboidal
produce short cells
storage parenchyma
Arrangement of Cambial Cells
fusiform initials
occur in horizontal rows
(a storied cambium)
or irregularly
w/o horizontal pattern
(nonstoried cambium)
Secondary Xyleml
Types of Wood Cells
cells on interior of vascular cambium
develop into secondary xylem
known as wood
wood may contain:
tracheids
vessel elements
fibers
sclereids
parenchyma
axial system
derived from fusiform initials
contains tracheary elements
radial system
develops from ray initials
hardwoods
of angiosperms & eudicots
strong & tough
softwoods
have few or no fibers
softer consistency
much harder than hardwoods
Growth Rings
early wood
first wood formed
spring wood
high proportion of wide vessles
ring porous
late wood
summer wood
lower proportion of vessels
annual rings
1 years growth
growth rings
diffuse porous
Heartwood & Sapwood
heartwood
dark wod
sapwood
lighter, moister outer region
formed each year by
vascular cambium
Reaction Wood
plants' response to stress
in angiosperms it is known as
tension wood
Outer Bark
Cork & Cork Cambium
cork cambium
also called phellogen
cells are cuboidal
produce cells that turn into phelloderm
cork cell
phellem cell
periderm
cork cambium
phelloderm
layers of cork cells
offers temporary protection
outer bark
tissues outside innermost cork cambium
inner bark
secondary phloem between:
vascular cambium
innermost cork cambium
Lenticels and Oxygen Diffusion
lenticels
regions of aerenchymatous cork
Bark becomes permeable to oxygen when
cork cambium produces cork cells
that become rounded as they mature
Initiation of Cork Cambia
timing is variable
can arise before twig/root is 1 yr old
can arise when it is several yrs old
may arise in a number of tissues:
epidermis
cortex
primary phloem
secondary phloem
Secondary Growth in Roots
A vascular cambium arises
just like the interfascicular cambium
The new vascular cambium has
same star shape as primary xylem
becomes round
some portions of the cambium are pushed outward
more rapidly than others
When a circular cambium is achieved
unequal growth stops & all parts grow at similar rates
Perennial roots also form bark
first cork cambium usually arises in the pericycle
causing the endodermis, cortex, and epidermis to be shed
Secondary Phloem
formed from vascular cambium
has axial & radial system
axial system responsible for:
conduction up & down root/stem
Anomalous Forms of Growth
Anomalous Secondary Growth
alternative cambia produce secondary bodies
that differ from the common type
Roots of Sweet Potatoes
amount of storage parenchyma increased
by an anomalous method of secondary growth
Numerous vascular cambia arise
around individual vessels or groups of vessels
Included Phloem
type of secondary phloem, located between two bands of xylem
Unequal Activity of the Vascular Cambium
The stem grows outward in two directions
but remains thin in the other two
becomes a thin, flat, woody ribbon
As the Bauhinia stem becomes wider
conducting capacity increases
flexibility remains about the same
Secondary Growth in Monocots
secondary vascular bundles
containing xylem and phloem
Columns of parenchyma cells undergo rapid division
& produce narrow cells that differentiate
Joshua tree
becomes tree-like
woody
vascular cambium arises outside outermost vascular bundles
Unusual Primary Growth
Palm trees
trunks do not taper at the tips
do not branch
primary tissue consisting of vascular bundles
distributed throughout ground tissue
establishment growth
increase in width & addition of adventitious roots in palms
form of primary growth
